1. Field of the Invention
The present invention relates to a dental cleaner material for removing a smear layer formed during cutting without injuring the tissue of a dentinal region, inter alia, dentine and, more particularly, to a cleaner material for cleaning cavities or the root canals.
2. Prior Art
In the preparation of a cavity in conservative dentistry, a dentinal region is partly cut away by dental abrasive materials such as diamond points or tungsten carbide bars. In this case, a part of dentine in the cavity is deposited onto the surface of dentine in the form of a layer comprising finely divided dentinal chips to form a deposit layer called the "smear layer". Such dentinal chips also enter into dentinal tubules and form dentinal plugs to close them up. Such a smear layer is said not only to mar the effect of pharmaceuticals applied thereto but also to lower the adhesion of a restorative material such as a composite resin to the dentinal region.
Due to difficulty encountered in the mechanical removal of the smear layer from within cavities with the use of a dental instrument, they have heretofore been eliminated by dissolving it in a dental etching material such as an aqueous solution of phosphoric or citric acid.
The smear layer is also found to be formed during the preparation of the root canal in endodontics by mechanical cutting with reamers, files or the like. The smear layer deposited onto the inner wall of the root canal contains therein residual pulpal tissue pieces and their decayed products as well as pus and microorganisms and their products, etc., which stimulate the tissue of the root canal end or mar the permeability and pharmacological effect of pharmaceuticals applied into the root canal, and further lower the adherence of a root canal filler to the root canal wall. In order to clean the interior of the root canal having its inner wall covered with such a smear layer, use has heretofore been made of pharmaceutical formulations based principally on sodium hypochlorite, phenol sulfonate and ethylenediaminetetraacetic acid (hereinafter abbreviated as "EDTA") as well as aqueous hydroxide peroxide.
When an aqueous solution of phosphoric or citric acid is used as the cavity cleaner, however, not only the smear layer deposited onto dentine but also the sound or healthy residual dentine are so dissolved therein that the cut ends of dentinal tubules are enlarged in the form of a funnel, and even collagen may be denatured by its strong acidity. The results are that the hypersensitivity of the dental pulp is induced; the monomer remaining in a composite resin or bacteria enter into the tubules; and the remaining sound dentine is too weakened to degrade the adherence of a restorative material.
Most of commercially available dental etching materials comprise an aqueous solution of phosphoric or citric acid to which highly dispersible silica (e.g., Aerosil R-380 manufactured by Nippon Aerosil Co., Ltd.) is added as a thixotropic material to improve workability, and there is a liklihood that highly dispersible silica particles may remain on the surface of the dentinal region, resulting in a lowering of the adherence of a restorative material, unless they are removed in water washing as carefully as possible.
Similarly, the smear layer is formed during the preparation of the root canal in endodontics. Such a layer has been removed by using mixed formulation of sodium hypochlorite with sodium hydroxide, about 10% aqueous solution of sodium hypochlorite, about 15% aqueous solution of EDTA, fomulation based principally on phenol sulfonate, aqueous hydroxide peroxide or the like. However, the mixed formulation comprising sodium hypochlorite and sodium hydroxide or about 10% aqueous solution of sodium hypochlorite may dissolve bacteria and the intra-root canal decayed products that are organic matters, but fail to dissolve the smear layer composed primarily of inorganic deposits. Further, about 15% aqueous solution of EDTA dissolve not only the smear layer but also sound dentine. Still further, careful attention should be paid to the use of phenol sulfonate formulations, since, although weaker than inorganic acids, they are acid so strong that they tend to be deposited onto parodontium (or soft tissue).